DRAM supply to stay ‘tight through 1996’

“Communication needs protocol stacks. Protocol stacks need operating systems. Operating systems and protocol stacks both need a lot of processing power, not to mention memory management units (MMU), Ethernet MACs and so on. User interfaces can also determine the need for compute-hungry operating system layers,” points out David Pashley, who runs the embedded development tools firm Direct Insight.

Fortunately, register-width is not necessarily reflected in chip price. “From 0.35µm and beyond, the cost differences between 16- and 32-bit start to disappear,” explains Manfred Schlett, manager of Renesas’ SuperH systems group. “There is now no reason for anyone to wait to use 32-bit. And if you’re not changing to 32-bit, your competitors will and they will offer much higher performance with a similar device cost,” he adds.

The message from STMicroelectronics, which has just announced its first ARM-based 32-bit microcontrollers, is similar. “Our objective is to make 16-bit micros unnecessary,” says ST’s microcontroller marketing director Colin Long.

There are hundreds of different 32-bit devices out there from dozens of families. And, as Pashley says: “Each has its own specific take on multimedia capability, offers greater or lesser digital signal processing (DSP) power, and sits on a different point on the low energy versus performance curve.

“Each pursues to a unique extent the goal of a single-chip solution and offers a particular permutation of on-chip peripherals from a list that includes display controllers, flash, RAM, Ethernet, USB, I²C, CompactFlash, UARTs, SPI and many more.”

And that’s without beginning to consider the available tools and software IP, which are all processor-specific.

Given this exhausting list, the best one can do is to look at some of the latest arrivals on the scene to get a snapshot of what’s around. ST’s STR710 new series, for example, is based on the 48MHz ARM7TDMI core and includes embedded flash and low pin-count packages.

This family, which starts at $6, is aimed at those who want the power and flexibility of a 32-bit microcontroller plus a large set of on-chip peripherals to help drive down system cost. For instance, there are up to ten communication interfaces including I2C, SPI, UART, CAN, USB, HDLC, MMC, and Smart Card interface.

Slightly more powerful is the STR720 series, which is based on the 66MHz ARM720T core ands includes cache, MMU, and SDRAM interface. It is for applications requiring performance and an open-system memory architecture that easily supports advanced operating systems. Both families target industrial control applications such as factory automation, point-of-sale and vending machines, as well as mass-market telecom applications such as bridges and protocol translators.

Renesas has introduced three new 32-bit micro cores over the last few months, and is busy rolling out all sorts of devices based on these and other established cores. The SH7641 and SH7618 are good examples of cost-optimised, mid-range next generation devices. The SH7641 is a 32-bit SuperH Risc microprocessor that features 144kbyte SRAM, 16kbyte cache memory and comprehensive peripheral functions including a multi-function timer unit for motor control. The SH7641 is based on the SH3-DSP CPU core and offers CPU performance of 130Mips and DSP performance of 200Mops at a maximum operating frequency of 100MHz.

The SH7618 is a 32-bit SH2-based micro that features both an Ethernet controller and a host interface to ease connection to another microprocessor. The device is designed for use in applications that require a network connection capability, including industrial equipment such as factory automation and surveillance cameras, audio/video products, for example DVD recorders, and air conditioners.

You could also look at embedded x86 micros. Development is PC-based and therefore straightforward, plus there is plenty of software around. The downside is that you don’t get all those integrated peripherals.

Power consumption has also tended to be on the heavier side. There are, however, devices like Transmeta’s Crusoe, which knock the power-consumption problem on the head. Crusoe is an x86-compatible software-based microprocessor that gives Gigahertz speeds without the need for active cooling and external fans. Integrated power management technology further improves the efficiency by dynamically scaling both the processor frequency and voltage according to the instantaneous demands of the computer system.

“In an embedded application, for example, you can turn the clock up and down 200 times a second,” explains Chris Russell, European operations manager for Transmeta. “If you want to incorporate DVD, LCD screens and embedded Windows XP, then this gives you all the performance you need but without requiring a fan.”

Crusoe devices are being designed into everything from speed cameras to gambling machines. And the newest additions to the family – the 5700 and 5900 series – can even be used on low cost four layer boards.

At the most exotic end of the 32-bit market, you could look at the Stretch S5000, an innovative software-configurable processor that can be changed according to application needs.

Based on the Tensilica Xtensa Risc processor core, the S5000 is the first micro to have programmable logic embedded inside the architecture, enabling developers to extend and optimise the instruction set at any time using C/C++. According to the latest figures from benchmarking organisation EEMBC, this $35 product beats the most powerful DSP-enhanced general-purpose processors and DSPs.

The final word goes to Pashley: “When migrating to 32-bit, the selecti on of off-the-shelf hardware and software is unquestionably more influential than the development activity that ensues, and arguably, the pivotal decision in the entire innovation process.”